The invention relates to a device for use with a subsea pump module which includes a housing, a pump disposed in the housing and having a pump inlet and a pump outlet, a pump shaft with mechanical seals and bearings for supporting the pump shaft in the housing, an electric pump motor arranged in the housing and having a motor shaft drive-connected to the pump shaft, which pump module has a pump motor lubrication/cooling circuit (a lubrication and coding circuit) exposed to the surrounding seawater and where the said pump inlet is at the side of the pump that is adjacent to the pump motor.
One of the requirements for subsea devices, such as a subsea pump module as mentioned, is that they should have a useful life of maximum length and with full functioning ability, even after they have been out of service for longer or shorter periods of time. In this connection, the integrity and functioning ability of the lubrication and cooling circuit will be of vital importance.
Clearly, therefore, there is a need for a subsea device of the said type that is reliable and has a long operative useful life.
Accordingly, it is an object of the present invention to provide a device for cooling and lubricating a subsea pump module as mentioned, and a specific object of the invention is to provide barriers and pressure differences relative to the fluid pressure in the pump in order thereby to ensure that any leaks are in the direction of the pump. In this way, in the case of a subsea pump module, the pump medium is prevented from contaminating the lubricant and coolant.
Another specific object of the invention is to provide a device for cooling and lubricating a subsea pump module in the form of an autonomous passive lubrication and cooling system without the need for external control systems or instrumentation under normal operating conditions, apart from condition monitoring which requires instrumentation, and means for refilling lubricant/coolant.
According to the invention, a device is proposed for use with a subsea pump module which includes a housing, a pump disposed in the housing and having a pump inlet and a pump outlet, a pump shaft with mechanical seals and bearings for supporting the pump shaft in the housing, an electric pump motor arranged in the housing and having a motor shaft drive-connected to the pump shaft, which pump module has a pump motor lubrication/cooling circuit exposed to the surrounding seawater, and where the said pump inlet is at the side of the pump that is adjacent to the pump motor, characterised in that the lubrication/cooling circuit is pressure-impacted by the pump medium pressure in front of the pump inlet via a separating means pretensioned towards the pump motor, and that an impeller is arranged on the pump shaft at the end adjacent to the pump inlet.
In this way a favourable balance of pressure is obtained, and by means of a suitable layout of the lubrication-cooling circuit with an impeller drive-connected to the electric motor there can advantageously be obtained a certain overpressure in the lubrication/cooling circuit towards the pump across the mechanical seals. It is especially advantageous, according to the invention, for the lubrication/cooling circuit to be pressure-impacted by said medium pressure via a separating diaphragm.
A separating diaphragm of this kind will provide a physical separation of the lubricant/coolant and the pump medium at the external point of pressure application.
It is particularly advantageous to provide/increase the said pressure application using a weight load which acts in the direction of the lubrication/cooling circuit.
A weight load of this kind will ensure/provide an overpressure in the lubrication/cooling circuit relative to the medium pressure.
It is particularly advantageous for the weight load to be in the form of a liquid column.
A heavy liquid column of this kind can be provided in a simple manner by using a heavy, preferably inert liquid.
A particularly favourable embodiment according to the invention is one where the liquid column is provided between an upper and a lower separating diaphragm.
In this way a double barrier is obtained.
It is especially advantageous for each individual separating diaphragm to be provided with a damper piston.
In one practical embodiment, the damper piston has a control rod attached thereto which passes through a seal that will interact with the damper piston if and when the diaphragm and thus the damper piston move towards an end position upon loss of volume in the separating diaphragm means. The use of a damper piston of this kind will protect the diaphragm in the event of such loss of volume.
In another embodiment according to the invention, the liquid column may be separated from the said medium and from the lubricant/coolant in the lubrication/cooling circuit by a respective float valve. In this connection, it is particularly advantageous to split the liquid column into two liquid columns which are separated from one another by a lubricant/coolant column, which is bounded at one of the liquid columns by a float valve.
It is especially advantageous to provide a seal lubrication circuit for the pump.
This seal lubrication circuit can advantageously be connected to the lubrication/cooling is circuit in such manner that the seal lubrication circuit has a pressure that is lower than that of the lubrication/cooling circuit, but higher than the said medium pressure.
A particularly favourable embodiment is one where the seal lubrication circuit is connected to the lubrication/cooling circuit via a separator for separating water from the lubricant/coolant, the separator being connected to the lubrication/cooling circuit at some point in the cooler.
A design of this kind allows a slight suction pressure to be obtained in the direction of the seal lubrication circuit, so that it is automatically refilled from the lubrication/cooling circuit via the separator.
In one embodiment, the seal lubrication circuit can be connected to the lubrication/cooling circuit via a separating diaphragm that is weight-loaded towards the lubrication/cooling circuit.
According to the invention, when separating diaphragms are used, each individual separating diaphragm can advantageously be associated with an external level sensor.
It is especially advantageous for the lubrication/cooling circuit to include an impeller in the electric motor.